This application claims priority of European Patent Application No. 99307104.2, which was filed on Sep. 7, 1999.
The invention relates to multiframe alignment in general and especially to a multiframe alignment for tandem connection trails at Non Intrusive Monitoring (NIM) Trail Termination (TT) sink functions and for TT sink functions in a Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) system.
The problem addressed with this invention typically arises in Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) systems in cases of protection switches within a Tandem Connection Trail. For a better understanding of SDH and SONET systems, reference is made to xe2x80x9cUnderstanding of SONET/SDHxe2x80x9d, ISBN 0-9650448-2-3, Andan Publisher, New Jersey.
In the before-mentioned network system a tandem connection is intended to provide an administrative monitoring domain which is operating independent of the end to end path. Rules for the establishment of a tandem connection trail are defined in ETSI EN 300 417-4-1 and ITU-T G.783.
The operation and also the establishment of a tandem connection trail shall influence the rest of the network system as less as possible. Under certain circumstances (i.e. if switching actions are performed within a tandem connection trail), current Tandem Connection Monitoring (TCM) implementations according to the current versions of the standards unnecessarily enlarge signal disturbances.
Accordingly, there is a need to reduce the influence of protection switches within a tandem connection trail in a Synchronous Digital Hierarchy (SDH) or in a Synchronous Optical Network (SONET) System by avoiding enlargements of signal disturbances caused by protection switches.
Detecting an aligned signal reception or an in multiframe signal transmission state subsequent to an interruption, distortion or switching operation of the signal transmission path on the basis of any received frame alignment signal (FAS) value avoids any undue interruption of the signal transmission caused by the insertion of all one""s while searching for the received frame alignment signal (FAS) only at a predetermined position.
If consequently a xe2x80x9cFAS found at presumed positionxe2x80x9d signal is replaced by a xe2x80x9cFAS foundxe2x80x9d signal and generated regardless of the position of a detected multiframe alignment signal and every detected multiframe alignment signal (FAS) is accepted as a valid frame alignment signal (FAS) then the shortest realignment time periods are realized.